MARGARETH KAZUYO KOBAYASHI DIAS FRANCO

MARGARETH KAZUYO KOBAYASHI DIAS FRANCO

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Synthesis of geopolymers for immobilization of radioactive waste using sewage treatment plant sludge
2021 - CASAS, A.; ARAUJO, L.; GARCIA, R.; VICENTE, R.; FRANCO, M.; MARUMO, J.
Effects of gamma radiation on cementitious materials in repository environment
2016 - FERREIRA, EDUARDO; VICENTE, ROBERTO; TURRILLAS, XABIER; YOKAICHIYA, FABIANO; FRANCO, MARGARETH; MARTINEZ, LUIS G.; CARVALHO, ALEXANDRE; MARUMO, JULIO T.
Cementitious materials are widely used in the management of radioactive waste and have to perform as required for the period of service life of the installation. In order to assess the long term durability of cement paste in a deep borehole for radioactive wastes, specimens were casted in laboratory and exposed to a gamma radiation field. The effects of the radiation in the specimens were evaluated by X-Ray Diffraction, as changes observed in the mineralogy and microstructure of the material after irradiation doses varying between 0 (without radiation) and 10 MGy. It was observed that the specimens exposed to higher doses of gamma radiation (up to 3MGy) presented differences between surface and core, when compared with the samples with no radiation or exposed to low doses. These results are important to model the behavior of cementitious materials under the conditions expected in a borehole repository and to provide data for the safety assessment of the installation.
Aplicação da química de radiação à questões tecnológicas do cimento relacionadas ao desenvolvimento de repositórios de rejeitos radioativos do modelo borehole
2019 - URBANI, G.L.; FRANCO, M.K.K.D.; YOKAICHIYA, F.; VICENTE, R.
Resíduos radioativos são usualmente descartados em repositórios do tipo borehole ou de superfície. Por questões de segurança, devem ser depositados em tambores e cobertos por cimento na sua destinação final. A radiação gama proveniente dos resíduos radioativos interage com a água livre da pasta de cimento e causa o fenômeno da radiólise. Essa interação que decompõe a água da pasta de cimento é estudada pela academia científica e ainda não é um consenso se a mesma afeta a resistência do concreto ou não. Para um melhor entendimento dessa questão, nesse estudo um modelo teórico simples é sugerido para quantificar a porcentagem da água que sofre radiólise e se essa perda é suficiente para afetar a resistência da barreira de cimento. O resultado indica que a quantidade de água perdida neste processo não é suficiente para diminuir a resistência do concreto. O modelo proposto foi aplicado para verificar os resultados experimentais, utilizando as condições iniciais expostas na literatura existente, com o propósito comparação e discussão sobre o fenômeno da radiólise.
A diffractometer project for Brazilian Multipurpose Reactor (RMB)
2019 - SOUZA, ALEXANDRE P.S.; OLIVEIRA, LUIZ P. de; YOKAICHIYA, FABIANO; GENEZINI, FREDERICO A.; FRANCO, MARGARETH K.K.D.
High-resolution di ractometer is one of the rst instruments of the set of 15 priority neutron scattering instruments to be installed at the Brazilian Multipurpose Reactor (RMB). A basic project of this instrument consists of the existence of three guides through which neutrons pass from source to sample to guarantee maximum neutron ux at the sample position. In this study we investigate guide geometry performance considering xed di ractometer geometry and spatial arrangement. Comparisons between di erent guide shapes and supermirrors are performed using software based on the Monte Carlo method, McStas. Our conclusion shows that a better solution is splitting the initial ux into two di erent guides to obtain the maximum ux at the sample position.
Study on s-shaped guide using McStas software
2019 - OLIVEIRA, LUIZ P. de; SOUZA, ALEXANDRE P. S.; YOKAICHIYA, FABIANO; GENEZINI, FREDERICO A.; FRANCO, MARGARETH K.K.D.
Monte Carlo simulations are performed for a vertical S-shaped neutron guide for the cold neutron sources of the FRM-II, HZB and PSI reactors through the McStas software. The aim of our study is investigate a relation between the cuto in the cold neutron spectrum and the sources. Results for the neutron ux at the sample position are presented for di erent supermirrors with m = 1, 2 and 3. The vertical S-shaped neutron guides additionally provide a vertical displacement between beam hole and sample position, which can facilitate the implementation and manipulation of sample environments.